Optical disc recording apparatus with efficient data checking

ABSTRACT

An optical disc recording apparatus which requires no additional head optical system and is capable of reducing the time required for a data checking operation. By detecting any irregularity of a signal in accordance with reflected light from an optical disc during the recording of the signal, it is determined whether the signal has been recorded correctly on the optical disc during the signal recording.

TECHNICAL FIELD

The present invention relates to an apparatus for recording signals onan optical disc.

BACKGROUND ART

In the past, it has been the practice with the optical disc recordingapparatus so that when signals are recorded on an optical disc, theoperation of confirming whether the written signals can be correctlyread out is performed for the purpose of enhancing the reliability ofthe signals recorded on the optical disc.

The most common one of the known methods is a method known as the RAW(read after write) check. According to this method, after the recordingof a signal on a certain data region of an optical disc or immediatelyafter the recording, the operation of reproducing the recorded signal isperformed so as to check the reproduced data and thereby to checkwhether the signal has been recorded correctly.

FIG. 6 is a block diagram showing the construction of a conventionaldevice for performing the RAW check. In FIG. 6, the laser beam emittedfrom a head 622 is first projected on an optical disc 621 and thereflected light from it is received by the photodetector in the head622. The resulting output signal from the photodetector is outputted asbinary coded data through a reproducing circuit 623 and a binarizationcircuit 624. In this way, the signal recorded on the optical disc 621 isread out in the form of binary coded data. This binary coded data isconverted into parallel data by a serial/parallel converter 625 and thedata read out is subjected to error correction by an ECC decordercircuit 626 thereby confirming whether the recorded signal can bereproduced as the correct data.

Also, it has been known in the past that the frequency band of anamplifier utilized for the detection of a servo signal for the servocontrol is sufficient if it is on the order of several KHz.

The servo control is "a control system so constructed that a controlledsystem follows up arbitrary changes of a desired value" and generallythe focusing control of the optical disc apparatus is such that a discsurface position is the desired value and the focal point of a laserbeam is caused to follow up this surface position. Also, in the case ofthe tracking control the desired value is the central position of a datarecording portion on the optical disc and a laser beam is projected onthis surface position thus causing the center of the resulting lightspot to follow up the surface position. A control element is mainlycomposed of an electric system so that the difference between thedesired value and the controlled system or the current position isconverted into an electric difference signal and the signal is sent tothe controlled system in the feedback system so as to reduce thedifference to zero.

Further, the servo controls employed by the optical disc recording andreproducing apparatus include for example a head movement control formoving the signal read/write head to the desired position, a focusingcontrol for positioning the focal point of light entering into andemerging from the head to a signal recording portion of the disc and atracking control for causing the focal point of the light to follow atrack on the disc and the signals used for these controls are servosignals.

With the above-mentioned conventional techniques, however, thereproducing operation for the data checking of the written signals isperformed after the writing operation during the signal recording andtherefore a long time is required as compared with the recordingoperation without the RAW check. While it is conceivable to add aseparate head which performs a reproducing operation for data checkingpurpose to overcome the problem of time consumption, there is thedisadvantage of requiring an additional head optical system.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide an optical discrecording apparatus which requires no additional head optical system andcapable of reducing the time required for a data checking operation.

To accomplish the above object, an optical disc recording apparatusaccording to a preferred aspect of the present invention includes:

signal recording means for recording a signal on an optical disc by theprojection of a laser beam,

a reflected light signal detecting circuit for generating a reflectedlight signal by receiving the reflected light from the optical discduring the recording of a signal, and

a decision circuit for detecting an irregularity of the reflected lightsignal to determine whether the signal has been normally recorded on theoptical disc.

It is preferable that the frequency band of the reflected light signaldetecting circuit is lower than the signal recording frequency.

An optical disc recording apparatus according to another preferredaspect of the present invention includes:

a head for recording a signal on an optical disc by projecting a laserbeam on the optical disc while subjecting the laser beam to intensitymodulation,

a photodetector for receiving the reflected light of the laser beam fromthe optical disc to convert the same into an electric signal,

a signal detecting circuit for receiving the signal from thephotodetector to generate a reflected light signal, and

an anomaly decision circuit for receiving the reflected light signal todetect an anomaly of the reflected light signal and thereby to determinewhether the signal has been recorded normally on the optical disc.

The frequency band of the signal detecting circuit should preferably belower than the intensity modulating frequency of the laser beam.

An optical disc recording apparatus according to still another preferredaspect of the present invention includes:

a head for recording a signal on an optical disc by projecting a laserbeam on the optical disc while subjecting the laser beam to intensitymodulation,

a photodetector for receiving the reflected light of the laser beam fromthe optical disc to convert the reflected light into an electric signal,

a servo signal detecting circuit for receiving the signal from thephotodetector to generate a servo signal for an auto focusing control,and

an anomaly decision circuit for receiving the servo signal to detect ananomaly of the reflected light signal and thereby to determine whetherthe signal has been recorded normally on the optical disc.

An optical disc recording apparatus according to still another preferredaspect of the present invention includes:

a head for recording a signal on an optical disc by projecting a laserbeam on the optical disc while intensity modulating the laser beam inaccordance with the recording signal,

a photodetector for receiving the reflected light of the laser beam fromthe optical disc to convert it into an electric signal,

a signal detecting circuit for receiving the signal from thephotodetector to generate a reflected light signal,

a comparison circuit for receiving the reflected light signal and therecording signal to compare the signals, and

an anomaly decision circuit responsive to an output from the comparisoncircuit to determine whether the signal has been normally recorded onthe optical disc.

An optical disc recording apparatus according to still another preferredaspect of the present invention includes:

signal recording means for recording a signal on a magneto-optical dischaving a GdFeCo reproducing layer and capable of direct overwriting byprojecting a laser beam on the disc,

a Kerr effect detector for detecting a Kerr effect of the reflectedlight from the optical disc during the signal recording, and

a decision circuit responsive to an output from the Kerr effect detectorto determine whether the signal has been normally recorded on theoptical disc.

An optical disc recording apparatus according to still another preferredaspect of the present invention includes:

a head for recording a signal on a magneto-optical disc having a GdFeCoreproducing layer and capable of direct overwriting by projecting alaser beam on the disc,

a Kerr effect detector for detecting a Kerr effect of the reflectedlight from the optical disc during the signal recording,

a photodetector for receiving the reflected light of the laser beam fromthe optical disc to convert it into an electric signal,

a signal detecting circuit for receiving the signal from thephotodetector to generate a reflected light signal, and

a decision circuit responsive to an output from the Kerr effect detectorand the reflected light signal to determine whether the signal has beennormally recorded on the optical disc.

Thus, the optical disc recording apparatus according to the presentinvention is designed so that by detecting an irregularity of a signalaccording to the reflected light from an optical disc during therecording of the signal, it is determined whether the signal has beennormally recorded on the optical disc during the signal recording.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing the construction of an optical discrecording apparatus according to a first embodiment of the presentinvention.

FIG. 2 is a block diagram showing the construction of an optical discrecording apparatus according to a second embodiment of the presentinvention.

FIG. 3 is a block diagram showing the construction of an optical discrecording apparatus according to a third embodiment of the presentinvention.

FIG. 4a, 4b, 4c and 4d are signal waveform diagrams showing the relationbetween the recording signal, the total reflected light signal and theoutput signal from the differential amplifier in the optical discrecording apparatus according to the third embodiment of the presentinvention.

FIG. 5 is a block diagram showing the construction of an optical discrecording apparatus according to a fourth embodiment of the presentinvention.

FIG. 6 is a block diagram showing the construction of a conventionalapparatus for performing the RAW check.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a block diagram showing the construction of an optical discrecording apparatus according to a first embodiment of the presentinvention. It is to be noted that in all the below-mentioned embodimentsincluding the present embodiment the optical disc used has a diameter of130 mm, a disc rotational speed of 1800 rpm and a record/reproduce laserbeam wavelength of 830 nm and the recording of a signal on a track atthe position of a disc radius R=45 mm is effected after the wholesurface of the optical disc has been initialized.

The recording of a signal on an optical disc 11 is effected byprojecting the laser beam emitted from a head 12 on the recordingsurface of the optical disc 11. The intensity of the laser beam ismodulated in accordance with the data in the signal to be recorded. Thefrequency (recording frequency) of the signal (recording signal)indicating the data to be recorded is generally in the range of 5 to 10MHz.

During the time that the signal is recorded on the optical disc 11, thereflected light of the laser beam from the disc surface is entered intoa quadsplit PD (photodetector) 13 through the head 12. As shown in theFigure, the quadsplit PD 13 is composed of four sensor portions A, B, Cand D and each of the sensor portions converts the incident light intoan electric signal of a level corresponding to its light intensity tooutput the signal. Each of the electric signals generated from thequadsplit PD 13 is applied to a summing amplifier 14 or 15. The signal(A+D) from the summing amplifier 14 is applied to one input terminal (+)of a servo signal detecting amplifier 16 and one input terminal of atotal reflected light signal detecting amplifier 17. Also, the signal(B+C) from the summing amplifier 15 is applied to the other inputterminal (-) of the servo signal detecting amplifier 16 and the otherinput terminal of the total reflected light signal detecting amplifier17.

An amplifier having a frequency band of 5 to 10 KHz is used as the servosignal detecting amplifier 16. For instance, if an amplifier having afrequency band of 5 KHz is used, signals of 5 KHz or less can bedetected. Similarly, an amplifier having a frequency band of 2 to 3 MHzis used as the total reflected light signal detecting amplifier 17. Forinstance, if an amplifier having a frequency band of 2 MHz is used,signals of 2 MHz or less can be detected.

The signal detected by the servo signal detecting amplifier 16 andhaving a frequency lower than the frequency band of 5 to 10 KHz is usedfor an auto focusing control and an auto tracking control. The signaldetected by the total reflected light signal detecting amplifier 17 andhaving a frequency lower than 2 to 3 MHz is applied to an anomalydecision circuit 18.

In accordance with the signal from the total reflected light signaldetecting amplifier 17, the anomaly decision circuit 18 determineswhether the signal has been recorded correctly on the optical disc 11.As mentioned previously, generally the recording frequency used forrecording signals on the optical disc is in the range of 5 to 10 MHz. Ifthe frequency band of the total reflected light signal detectingamplifier 17 is selected lower than the recording frequency, no signalsof 5 to 10 MHz are generated from the total reflected light signaldetecting amplifier 17 so far as the recording has been effectednormally. Therefore, when a signal of a frequency lower than 2 to 3 MHzis detected from the total reflected light signal detecting amplifier17, it is considered that the total reflected light signal is irregular.At this time, the anomaly decision circuit 18 determines that therecording has not been effected normally and an output signal of thecorresponding content is generated.

The signal indicating the result of the decision by the anomaly decisioncircuit 18 is applied to a recording control circuit 19. When it isdecided that there has been an anomaly during the recording, therecording control circuit 19 controls a reperformance of the recordingoperation on the optical disc 11. For instance, the operation of thehead 12 is controlled so that the projection position of the laser beamon the optical disc 11 is moved to the position required forreperformance of the recording operation and the signal to be recordedis again sent to the head 12.

With the frequency band of the total reflected light signal detectingamplifier 17 set to 2 MHz, the presence of irregularity in the totalreflected light signal was actually checked during the signal recordingthus detecting the portion in which the signal was not recordedcorrectly.

Thus, by detecting the presence of irregularity in the total reflectedlight signal during the signal recording, there is no need to performthe reproduction required for checking the recorded signal after thesignal has been recorded or immediately after the recording of thesignal.

FIG. 2 is a block diagram showing the construction of an optical discapparatus according to a second embodiment of the present invention. InFIG. 2, the signal having a frequency lower than 5 to 10 KHz anddetected by a servo signal detecting amplifier 16 is used for an autofocusing control and it is also applied to an anomaly decision circuit21. The anomaly decision circuit 21 detects a signal of a frequencylower than 5 to 10 KHz. A low-pass filter may for example be used forsuch anomaly decision circuit.

When the auto focusing servo is functioning normally, practically nosignal is generated from the servo signal detecting amplifier 16. On theother hand, when the focusing servo is not functioning normally or whenthere is any defect on an optical disc 11, a signal having a certainlevel is generated from the servo signal detecting amplifier 16. Also,when such signal is generated, a detection signal is also generated fromthe anomaly decision circuit 21. Since it is considered that therecording has not been effected normally if the focusing servo is notfunctioning normally or if there is any defect on the optical disc 11, arecording control circuit 19 controls a reperformance of the recordingoperation on the optical disc 11 in accordance with the detection signalfrom the anomaly decision circuit 21 in the like manner as the firstembodiment.

The frequency band of the anomaly decision circuit 21 is sufficient ifit is equivalent to the frequency band of the servo signal detectingamplifier 16 and it need not be higher than the frequency band of theservo signal detecting amplifier 16.

In the present embodiment, the frequency of a signal to be detected bythe anomaly decision circuit 21 is lower than 5 to 10 KHz. On the otherhand, the recording frequency of the signal is between 5 and 10 MHz.Thus, in the case of a very short-time recording operation which recordsa signal for a short data on the optical disc 11, there are cases whereit is impossible to detect an anomaly even if there is any. The anomalydetection of the present embodiment is suited for detecting theoccurrence of anomaly over a relatively wide area on the disc 11 whenrecording a signal for a long continuous data on the disc 11.

In addition, the amplifier for generating a focusing error signal in theconventional apparatus may be used for the servo signal detectingamplifier 16 of the present embodiment. By adding the anomaly decisioncircuit 21 to the output side of this amplifier, it is possible torealize the apparatus of the present embodiment.

FIG. 3 is a block diagram showing the construction of an optical discapparatus according to a third embodiment of the present invention. Inthe third embodiment, the frequency band of a total reflected lightsignal detecting amplifier 17 is 10 MHz.

Then, when recording a signal on an optical disc 11 as mentionedpreviously, a laser beam is intensity modulated by the recordingfrequency of the signal. In other words, the laser beam is turned on andoff at the recording frequency. If the frequency band of the totalreflected light signal detecting amplifier 17 is increased excessively,variations in the total reflected light signal due to the turning on andoff of the laser beam will also be detected.

Thus, the present embodiment includes a delay circuit 31 for delayingthe recording signal (the signal indicative of the data to be recorded)a predetermined time. The delay time by the delay circuit is set so asto correspond to the time interval between the generation of therecording signal and the generation of a total reflected light quantitysignal corresponding to the recording signal.

The recording signal passed through the delay circuit 31 is applied toone input terminal (+) of a differential amplifier 32. The totalreflected light signal from the total reflected light signal detectingamplifier 17 is applied to the other input terminal (-) of thedifferential amplifier 32. In other words, the recording signal and thetotal reflected light signal are applied in coincidence with each otherin timing to the differential amplifier 32 and the differentialamplifier 32 generates the difference signal of the two input signals.

FIGS. 4a to 4d are signal waveform diagrams showing the relation betweenthe recording signal, the total reflected light signal and the outputsignal of the differential amplifier 32 in the third embodiment.

FIG. 4a shows an example of the waveform of the recording signal (theoutput signal from the delay circuit 31), and the output signal from thedelay circuit 31 and the total reflected light signal from the totalreflected light signal detecting amplifier 17 are the same in waveformwhen the data has been normally recorded on the disc 11. As a result,the output signal from the differential amplifier 32 shows a zero outputstate as shown in FIG. 4b.

FIG. 4c shows an example of the waveform of the total reflected lightsignal from the total reflected light signal detecting amplifier 17under the anomalous condition.

When the recording of the signal is anomalous in this way, a signal ofthe waveform (FIG. 4d) corresponding to the difference between thewaveform (FIG. 4c) of the total reflected light signal and the waveform(FIG. 4a) of the recording signal from the delay circuit 31 is generatedfrom the differential amplifier 32. The signal of the waveform shown inFIG. 4d is applied to an anomaly decision circuit 33 so that it iscompared with a predetermined threshold value and it is determined asthe result of this discrimination operation of the anomaly decisioncircuit 33 that the recording on the disc 31 has not been effectednormally. When the anomaly decision circuit 33 generates an outputrepresenting the occurrence of the anomaly, a recording control circuit19 receives the output and it controls the reperformance of therecording operation as mentioned previously.

FIG. 5 is a block diagram showing the construction of an optical discapparatus according to a fourth embodiment of the present invention. InFIG. 5, a disc 51 is a magneto-optical disc having a GdFeCo reproducinglayer and capable of direct overwriting. The description on themagneto-optical disc having a GdFeCo reproducing layer and capable ofdirect overwriting is included on pages 65 to 72 of The Institute ofElectronics, Information and Communication Engineers "Technical Reportof IEICE" MR 92-94 (1993-3).

Generally, in the magneto-optical disc having a GdFeCo reproducing layerand capable of overwriting the curie point temperature of the GdFeCoreproducing layer is set higher than the curie point temperature of thememory layer due to the composition of the reproducing layer. Therecording signal assumes two kinds of values according to the directionsof magnetization of the recording layer so that the directions ofmagnetization of the recording layer are first transferred to the memorylayer and then are transferred to the GdFeCo reproducing layer, therebyeffecting the recording.

The directions of magnetization of the GdFeCo reproducing layer are inconformity with the directions of magnetization of the memory layerwithin the range from the room temperature to near the curie pointtemperature. When the laser beam is projected on the magneto-opticaldisc 51, the memory layer reaches the curie point temperature so thatthe directions of magnetization are transferred to it from the recordinglayer and immediately thereafter the directions of magnetization aretransferred to the GdFeCo reproducing layer.

At this time, the Kerr effect can be detected by the reflected lightfrom the magneto-optical disc 51. If the Kerr effect cannot be detected,it can be determined that the signal has not been recorded normally onthe optical disc 51.

During the time that the signal is recorded on the magneto-optical disc51, the reflected light from the optical disc 51 is entered into aquadsplit PD 13 through a head 12. The flow of the signals from thequadsplit PD 13 up to a servo signal detecting amplifier 16 and a totalreflected light quantity signal detecting amplifier 17 is the same as inthe case of the first embodiment. Further, the reflected light from thehead 12 is also entered into a PD 52 through a light-sensitive element55.

The light-sensitive element 55 is an optical member which passes onlylight of a predetermined polarizing direction. In the presentembodiment, it is only necessary to design so that the light-sensitiveelement 55 passes only light of a polarizing direction when thereflected light has not been subjected to the Kerr effect. If it is sodesigned, when the reflected light is subjected to the Kerr effect, thepolarizing direction is changed and thus the reflected light cannot bepassed through the light-sensitive element 55. As a result, thereflected light is not entered into the PD 52 and no signal is generatedfrom the PD 52, thereby causing a Kerr effect detecting amplifier 53 togenerate no signal.

On the other hand, when the reflected light is not subjected to the Kerreffect, the reflected light is passed through the light-sensitiveelement 55. The light passed through the light-sensitive element 55 isentered into the PD 52 and thus an electric signal corresponding to theincident light quantity is generated from the PD 52. The output signalfrom the PD 52 is amplified by the Kerr effect detecting amplifier 53and then applied to an anomaly decision circuit 54.

As described hereinabove, when the reflected light is not subjected tothe Kerr effect, a signal is applied to the anomaly decision circuit 54so that the signal is discriminated by the anomaly decision circuit 54and it is determined that the data has not been recorded normally on theoptical disc 51. When the occurrence of the anomaly is detected in thisway, the operation of a recording control circuit 19 is the same as inthe case of the other embodiments described previously.

Further, the total reflected light signal from the total reflected lightsignal detecting amplifier 17 is also applied to the anomaly decisioncircuit 54. Similarly as the first embodiment, the present embodiment isalso capable of determining whether the recording has been effectednormally according to the total reflected light signal.

In addition, the anomaly decision circuit 54 can be so constructed thatan anomaly of the recording operation is determined when a signal isapplied from at least one of the total reflected light signal detectingamplifier 17 and the Kerr effect detecting amplifier 53.

With the optical disc apparatus according to the present embodiment,confirmation was made of the operation of recording a signal of a 7 MHzrecording frequency at the position of a radius R=45 mm of anoverwritable optical disc having a GdFeCo reproducing layer. In thisapparatus, the frequency bands of the total reflected light signaldetecting amplifier 17 and the Kerr effect detecting amplifier 53 wereeach 10 MHz. As a result, during the recording of signals on the opticaldisc the presence of any anomolous recorded signal was clearly detectedin a real time manner so that upon the detection the head was moved tothat position where the recording was to be effected anew and therecording operation was performed again, thereby eventually recordingagain the signal normally on the disc through the series of continuousoperations.

It is to be noted that while the present embodiment is equivalent to theoptical disc apparatus of the first embodiment plus the light-sensitiveelement 55, the PD 52 and the Kerr effect detecting amplifier 53, it isneedless to say that the same results can be obtained by adding thelight-sensitive element 55, the PD 52 and the Kerr effect detectingamplifier 53 to the optical disc apparatus of the second and thirdembodiments, respectively.

From the foregoing description it will be seen that in accordance withthe present invention, when a signal has not been recorded correctly onan optical disc, this can be detected upon recording of the signal.Thus, there is no need to perform anew a reproducing operation for datachecking purposes after the signal has been recorded with the resultthat not only any waste of additional time for this purpose can beavoided but also there is no need to provide any additional opticalsystem for such reproducing operation.

Further, in the case of a magneto-optical disc recording apparatuscapable of direct overwriting, no erasing operation is required from theoutset so that the application of the present invention not onlyentirely eliminates the time required to perform a reproducing operationfor data checking purposes after the signal recording but alsoabsolutely eliminates the need to provide an additional optical systemfor such purposes, and this fact constitutes a further advantageouspoint.

We claim:
 1. An optical disc recording apparatus comprising:a signalrecording device for recording a signal on an optical disc by projectinga laser beam on said optical disc, a reflected light signal detectingcircuit for receiving reflected light from said optical disc duringsignal recording thereon to generate a reflected light signal, and adecision circuit for detecting an irregularity of said reflected lightsignal to determine whether said signal has been normally recorded onsaid optical disc, wherein a frequency band of said reflected lightsignal detecting circuit is lower than a signal recording frequency. 2.An optical disc recording apparatus comprising:a head for recording asignal on an optical disc by projecting a laser beam on said opticaldisc while subjecting said laser beam to intensity modulation, aphotodetector for receiving reflected light of said laser beam from saidoptical disc to convert the reflected light into an electric signal, asignal detecting circuit for receiving the signal from saidphotodetector to generate a reflected light signal, and an anomalydecision circuit for receiving said reflected light signal to detect ananomaly of said reflected light signal and thereby to determine whethersaid signal has been normally recorded on said optical disc, wherein afrequency band of said signal detecting circuit is lower than anintensity modulation frequency of said laser beam.
 3. An optical discrecording apparatus comprising:a head for recording a signal on anoptical disc by projecting a laser beam on said optical disc whilesubjecting said laser beam to intensity modulation, a photodetector forreceiving reflected light of said laser beam from said optical disc toconvert said reflected light into an electric signal, a servo signaldetecting circuit for receiving the signal from said photodetector togenerate a servo signal for an auto focusing control, and an anomalydecision circuit for receiving said servo signal so as to detect ananomaly of said servo signal and thereby to determine whether saidrecording signal has been recorded normally on said optical disc,wherein a frequency band of said servo signal detecting circuit is lowerthan an intensity modulation frequency of said laser beam.
 4. An opticaldisc recording apparatus comprising:a head for recording a recordingsignal on a magneto-optical disc having a GdFeCo reproducing layer andcapable of direct overwriting by projecting a laser beam on saidmagneto-optical disc, a Kerr effect detector for detecting a Kerr effectof reflected light from said magneto-optical disc during signalrecording, a photodetector for receiving the reflected light from saidmagneto-optical disc to convert said reflected light into an electricsignal, a signal detecting circuit for receiving the electric signalfrom said photodetector to generate a reflected light signal, and adecision circuit responsive to an output from said Kerr effect detectorand said reflected light signal to determine whether said recordingsignal has been recorded normally on said magneto-optical disc.